In an exposure apparatus, a structure in which an alignment system and an exposure system are formed independently of each other and a plane motor is employed as a positioning stage is disclosed in Japanese Patent Laid-Open No. 2001-217183. FIG. 8 is a view showing a stage device in the exposure apparatus disclosed in Japanese Patent Laid-Open No. 2001-217183.
Referring to FIG. 8, reference symbol PL denotes a projection optical system; and ALG, an alignment optical system. A stator 112 as a base has a measurement (alignment) region and an exposure region. Two movable stages (WST1 and WST2) can move in the measurement region and exposure region independently of each other. In this exposure system, exposure and alignment measurement can be performed simultaneously so that the throughput can be improved.
The plane motor has a magnet group (not shown) arrayed on the lower surfaces of the movable stages (WST1 and WST2) and a coil group 98 arrayed in a matrix in the stator 112. The Lorentz force generated by the mutual operation of the magnetic fluxes of the magnet group and a current flowing through the coil group can move the movable stages (WST1 and WST2) relative to the stator 112.
FIG. 7 shows the coil cooling structure of a plane motor disclosed in Japanese Patent Laid-Open No. 2001-175434. The coil group of the plane motor stator is sealed by a stator main body 32. In FIG. 7, a refrigerant is supplied from 88A (88B) and discharged from 92A (92B) to cool the coil group in the stator.
Generally, a stage operation for performing alignment measurement and a stage operation for performing exposure are often different from each other. In an exposure process, scanning must be performed for every shot of the exposure target. Thus, the stage moves uniformly to a certain degree through the entire region. In alignment measurement, the movement required of the stage varies depending on the accuracy to be obtained and a measuring method. Therefore, usually, the energization amount for the coil group arranged in the exposure region and that for the coil group arranged in the measurement region are different and, naturally, the heat values of the two coil groups are expected to be different.
For example, in the alignment measurement, assume that a scheme that does not measure the entire wafer, but measures only a certain representative point, is employed. The movement of the stage required in the alignment measurement may be smaller than that required in the exposure region, and the energization amount and energization time of the coils are accordingly smaller than those for the coils in the exposure region. Therefore, the heat amount of the coil group in the measurement region becomes smaller than that in the exposure region. In short, heat generation of the coil group in the stator largely differs between the two regions.
For this reason, in an exposure apparatus having two independent regions, i.e., an exposure and a measurement region, as in the device in FIG. 8, if the coil group in the stator is cooled collectively, as in the device in FIG. 7, the cooling efficiency is expectedly poor. Usually, the flow rate of the refrigerant flowing through a refrigerant pipe 89A (89B) of FIG. 7 is set such that the temperature of the refrigerant becomes equal to or less than allowable temperature with respect to a coil with the largest heat generation.
In the structure in which the coil group in the stator is cooled collectively, if variations in coil heat generation are large, a coil with small heat generation is cooled by an excessively large amount of refrigerant. As a result, although a large amount of refrigerant is supplied as a whole, the maximum coil temperature cannot be suppressed easily.